The present invention relates to a process for the preparation of bis- and tris-(3-dimethylaminopropyl)-amine by catalytic hydrogenation of 3-(dimethylamino)-propionitrile. In this connection, palladium catalysts are employed on an Al.sub.2 O.sub.3 -containing support.
Bis- and tris-(3-dimethylaminopropyl)-amines are important auxiliaries for the preparation of polyurethane foams (DE-OS German Published Specification) 3,048,832, DE-OS (German Published Specification) 2,624,528, U.S. Pat. No. 4,255,528, U.S. Pat. No. 4,431,753). The preparation of bis-(3-dimethylaminopropyl)-amine is described, for example, in U.S. Pat. No. 4,101,466, U.S. Pat. No. 4,143,071 and DE-OS (German Published Specification) 3,048,832. However, only low product yields are obtained in all cases or the selectivity is only satisfactory with a low conversion. The purification of the product is consequently complicated and unsuitable for an industrial process.
The preparation of tris-(3-dimethylaminopropyl)-amine is described, for example, in DE-PS (German Patent Specification) 2,624,528. N,N-bis-(3-dimethylaminopropyl)-propylene-1,3-diamine is methylated here with formaldehyde in the presence of formic acid according to Leuckart-Wallach. However, this method of preparation starts from an expensive intermediate and requires corrosive and aggressive chemicals.
According to J. Chem. Soc. (A) 1971, 2024, the tertiary amine mentioned in the above paragraph is prepared by reaction of tris-(3-hydroxypropyl)-amine with thionyl chloride and subsequently with an excess of dimethylamine. The duration of the reaction of 24 hours is very long. For working-up, excess 40% strength potassium hydroxide solution is added to the reaction solution and it is extracted with ether. This method of preparation is impracticable from the industrial and ecological point of view. Yields are also not mentioned.
Thus, there is therefore no reaction path described for the preparation of the substances mentioned in the title which starts from simple and economical compounds and yields the tertiary amine in good yields. A need for such a process thus existed.